DDT residues in the soil of an extensive salt marsh on the south shore of Long Island averaged more than 13 pounds per acre (15 kilograms per hectare); the maximum was 32 pounds per acre (36 kilograms per hectare). A systematic sampling of various organisms from the vicinity showed concentrations of DDT increasing with trophic level through more than three orders of magnitude from 0.04 part per million in plankton to 75 parts per million in a ring-billed gull. Highest concentrations occurred in scavenging and carnivorous fish and birds, although birds had 10 to 100 times more than fish. These concentrations approach those in animals dying from DDT poisoning, which suggests that many natural populations in this area are now being affected, possibly limited, by DDT residues. Similar concentrations have been reported elsewhere in North America.

https://science.sciencemag.org/content/sci/156/3776/821.full.pdf

DDT Residues in an East Coast Estuary: A Case of Biological Concentration of a Persistent Insecticide

The persistence, sources, fate and possible control of pesticides are reviewed and discussed. The amounts of pesticides in soil, air, freshwater, seawater, soil and aquatic invertebrates, plants, fish, birds, other vertebrates, human food and human beings are summarized. The ways the amounts of these residues can be decreased are discussed.

Persistent pesticides in the environment

: A detailed description is given of the community structure and ecosystem processes of the mangrove forests of south Florida. Information covered ranges from details of mangrove distribution, primary production, and diseases to aspects of reproduction, biomass partitioning, and adaptations to stress. Mangrove ecosystems are considered in terms of zonation, succession, litter fall and decomposition, carbon export, and energy flow. Most of the components of mangrove communities are cataloged and discussed; these include microorganisms, plants other than mangroves, invertebrates, fishes, reptiles, amphibians, birds, and mammals. Finally, two sections summarize the value of mangrove ecosystems to man and present ways to manage this type of habitat.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a323074.pdf

The Ecology of the Mangroves of South Florida: A Community Profile

Concentrations of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] as low as a few parts per billion in water reduced photosynthesis in laboratory cultures of four species of coastal and oceanic phytoplankton representing four major classes of algae, and in a natural phytoplankton community from Woods Hole, Massachusetts. Toxicity to diatoms increased as cell concentration decreased. This inhibition may be of ecological importance.

DDT reduces photosynthesis by marine phytoplankton.

The spatial size distribution of grunts and snappers have previously indicated the separation of juveniles in nursery habitats from the adults on the coral reef. This implies life cycle migrations from nursery habitats (such as seagrass beds and mangroves) to the coral reef. If diet shifts are related to such migrations, then the diets of these fish must change before or around the fish size at which such migrations take place. A wide size range of juveniles of two grunt species ( Haemulon sciurus and Haemulon flavolineatum ) and of two snapper species ( Lutjanus apodus and Ocyurus chrysurus ) were caught in seagrass beds and mangroves, and their gut contents identified and quantified. Regression analysis between fish size and dietary importance of small crustaceans showed a negative relationship in all four species. Positive relations were found for H. sciurus , L. apodus and O. chrysurus between fish length and the dietary importance of decapods, and for L. apodus and O. chrysurus between fish length and prey fish importance. Critical changes in the fish diets with fish size were examined by application of a Canonical Correspondence Analysis (CCA). The CCA yielded three clusters of size-classes of fishes with similar diets, and application of a Mantel test showed that each of these clusters had significantly different diets, and that each cluster diet was significantly specialised. The size at which a fish species ‘switched’ from one cluster to another was compared with size-at-maturity data and with the typical size at which these species migrate from the nursery habitats to the coral reef. H. sciurus and H. flavolineatum may be prompted to migrate from the nursery habitats to coral reef habitats because of dietary changes, or because of the development of the gonads. For L. apodus and O. chrysurus , a dietary changeover forms a more likely explanation for nursery-to-reef migrations than does sexual maturation because these species reach maturity at sizes much larger than the maximum size of individuals found in nursery habitats. Although other factors may theoretically initiate or promote the migration patterns, the results of this study indicate that ontogenetic dietary changes may crucially influence the nursery-to-coral reef migrations of these reef fish species.

Diet shifts of Caribbean grunts (Haemulidae) and snappers (Lutjanidae) and the relation with nursery-to-coral reef migrations

A tidal marsh ditch near Pensacola, Florida was treated with 0.2 pound of DDT per acre in March 1963, and observed for 4 months. Ninety-eight per cent of the animal mortality occurred within 3 weeks after treatment. A population of cyprinodont fish was restored by reproduction of surviving and introduced fish. DDT was detected in surface water samples 8 days after treatment but not after 14 days, while DDT was not detected in bottom water samples later than 1 day after treatment. Seven weeks after treatment, vegetation samples averaged 9.1 ppm of DDT, after reaching a maximum of 75 ppm of DDT 3 to 4 weeks after treatment. Sediment samples yielded more variable residues, averaging 0.76 ppm of DDT at 7 weeks after reaching a maximum of 3.35 ppm of DDT 6 weeks after treatment. Fish accumulated up to 90 ppm of DDT within 5 weeks after treatment. Highest DDT residues detected in fiddler crabs and snails ranged from 15 to 25 per cent of the average residues detected in fish. The net water movement as i...

Kinetics and Effects of DDT in a Tidal Marsh Ditch

A study of the biology of the gray snapper was based on the examination of 849 fish collected primarily from the sport fishery of Everglades National Park. Gray snappers from Park waters ranged from 1 to 5 years of age, with age-groups II and III making up 62 and 29 percent of the catch. Mean lengths for each age group, age and length at recruitment into the sport fishery, length-weight relationship, and sex ratio of gray snapper are given. All Everglades Park fish were immature. The stomachs of 200 fish were examined for food contents. Crustaceans made up 61.6 percent of food items by number and 76.7 percent by volume, shrimp occurring most frequently. Fish and crabs occurred in 34 and 27 percent of the stomachs containing food.

Robert A. Croker

Papers

Kinetics and Effects of DDT in a Tidal Marsh Ditch

Growth and Food of the Gray Snapper, Lutjanus griseus in Everglades National Park